1. Field
The presently disclosed embodiment relates to a system for conditioning and sweeping cryogenic propellant circuits of an aircraft.
In the context of the presently disclosed embodiment, an aircraft is understood to mean any vehicle able to move around in the earth's atmosphere and in space and that comprises at least one cryogenic fluid circuit notably for powering a rocket motor. It may notably be an aircraft with a hybrid aerodynamic and single-stage space flight, such as described in document FR 2 907 422 A1 in the name of the applicant company, a two-stage vehicle or a vehicle comprising a carrier airplane and a spaceplane launched from the carrier airplane.
2. Brief Description of Related Developments
The cryogenic propellant circuits used for the propellants of rocket motors, piping and ancillary devices notably of launchers or space aircraft cannot be left in contact with the ambient air because the moisture contained in this air freezes upon contact with the circuits.
In the case of very low temperature circuits, for example circuits carrying liquid hydrogen, the oxygen in the air will also be able to liquefy and build up, with the associated risks of fire and explosions that that implies.
Likewise, it is necessary to remove the gases derived from any leaks on these circuits and to avoid any contaminating of the environment surrounding the circuits with these gases.
In order to avoid these problems it is known practice to circulate nitrogen or helium continuously and at a pressure above atmospheric pressure around these circuits as long as the vehicle is on the ground. Such a method for protecting the cryogenic circuits by sweeping with a gas is known as conditioning.
Space launchers using cryogenic-propellant propulsion systems have a flight time through the atmosphere that is very short of the order of a few tens of seconds, thereby limiting the exposure of the circuits to atmospheric air during this flight.
The checking and conditioning of the environment of the cryogenic circuits is therefore carried out on the ground, right before the tanks are filled, using a conditioning circuit connected to the launcher. This conditioning continues until launcher takeoff but the conditioning-gas supply devices are disconnected upon launcher takeoff.
The conditioning circuit continuously sweeps the launcher zones containing cryogenic circuits and tanks with dry nitrogen in the event that the propulsion does not use liquid hydrogen, or helium when hydrogen is used, the nitrogen or the helium coming from an installation on the ground.
The conditioning circuits also collect any leaked propellant.
On the other hand, they no longer need to be fed with liquid during atmospheric flight of the launchers because the rapid ascent of these vehicles through the atmosphere leads to emptying of the internal compartments because of the rapid drop in external pressure.
This drop in pressure means that there is also no ingress of external air into the relevant compartments of these aircraft.
The situation of an aircraft of the spaceplane type using rocket motor propulsion using LOx/liquid methane cryogenic liquid propellants or semicryogenic liquid propellants with liquid oxygen is entirely different.
This is because a spaceplane will have a cruising phase lasting several tens of minutes in the atmosphere and it then becomes necessary to continue to sweep and condition the cryogenic propellant circuits during atmospheric flight.
Such a device and the associated conditioning gas become very penalizing in terms of dry weight both on account of the storage tanks and on account of the mass of conditioning gas.